System, apparatus and method for synchronizing communications between devices

ABSTRACT

Systems, apparatuses and methods for synchronizing communication actions between multiple communication devices by accounting for discrepancies between timing functionality in communicating devices. A time value indicative of a remote device&#39;s view of current time is received. Where it is determined that the time value differs from a locally generated view of current time by at least an established amount, the range of time in which communications signals with the remote device will be monitored and transmitted is extended.

This is a continuation of co-pending U.S. patent application Ser. No.12/564,682, filed Sep. 22, 2009, and entitled “SYSTEM, APPARATUS ANDMETHOD FOR SYNCHRONIZING COMMUNICATIONS BETWEEN DEVICES”, which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates in general to communications, and moreparticularly to systems, apparatuses and methods for synchronizingcommunication actions between multiple communication devices.

BACKGROUND OF THE INVENTION

Systems employing numerous devices often require or otherwise benefitfrom the ability for these devices to communicate with one another.While each device may have its own purpose and responsibilities, theymay need to transmit information to, and/or receive information from,other devices of the system. Device-to-device communication may beaccomplished by wiring the devices together, and communicating via thewires. Systems today are continually moving towards wirelesscommunication, which generally makes installation more convenient, andamong other things provides greater flexibility and scalability.

Whether devices communicate wirelessly or otherwise, the communicatingdevices may communicate at some time that is made known to each of thecommunicating devices. For example, if a sending device is to send amessage to a targeted receiving device(s) at a particular time or when aparticular event occurs, and the targeted receiving device(s) is tomonitor for the message at that particular time or when the eventoccurs, then the communicating devices may need to have a cooperativereference of time.

A more particular scenario is provided. One drawback to wirelesscommunication is that information transfer is not confined to a wire, asin a direct wired system. Rather, the information is transmitted overthe air, and transmissions from neighboring systems can interfere withsystem communications. To address this issue, wireless network systemshave employed various methods of transmitting radio signals, such asfrequency hopping. Frequency hopping generally refers to a modulationtechnique where the signal carrier is rapidly switched among manyfrequency channels. Each party to the communication must know thefrequency hopping sequence in order to know when it is to transmit at acertain frequency in the sequence. Using the frequency hopping sequence,transmitting devices can properly address targeted devices, andreceiving devices can reject information from neighboring devices thatare not within their system but within their reception range. However,to know when the particular communication frequency will be active, boththe transmitting and receiving devices may need to utilize a timer(s) orother timing functionality. Imprecise component tolerances in thevarious communication devices will lead to relative timing imprecisionsin determining when the communication devices should monitor forincoming messages and/or signal outgoing message transmissions. Theseimprecisions can lead to communication errors.

Accordingly, there is a need in the communications industry for systemsand methods for recognizing discrepancies in relative timing betweencommunicating devices, and taking action to correct or otherwise accountfor such discrepancies to maintain proper communication functionality.It is also beneficial to iteratively increase the accuracy between thetiming functionality of the communicating devices. The present inventionfulfills these and other needs, and offers other advantages over theprior art.

SUMMARY

To overcome limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosessystems, apparatuses and methods for synchronizing communication actionsbetween multiple communication devices.

In accordance with one embodiment, a method is provided for accountingfor discrepancies between timing functionality in communicating devices.A time value indicative of a remote device's view of current time isreceived. Where it is determined that the time value differs from alocally generated view of current time by at least an establishedamount, the range of time in which communications signals with theremote device will be monitored and transmitted is extended.

According to more particular embodiments of such a method, extending therange of time involves initiating monitoring for incoming signals at atime earlier than an expected start time as determined from the locallygenerated view of current time. In another embodiment, extending therange of time involves discontinuing monitoring of incoming signals at atime later than an expected termination time as determined from thelocally generated view of current time. According to more particularembodiments of such a method, extending the range of time involves bothinitiating monitoring for incoming signals at a time earlier than anexpected start time as determined from the locally generated view ofcurrent time, and discontinuing monitoring of the incoming signals at atime later than an expected termination time as determined from thelocally generated view of current time.

According to still other particular embodiments of such a method,extending the range of time involves initiating transmission of amessage preamble for outgoing signals at a time earlier than an expectedstart time as determined from the locally generated view of currenttime. In another embodiment, extending the range of time involvesdiscontinuing transmission of a message preamble for outgoing signals ata time later than an expected termination time as determined from thelocally generated view of current time. In still another embodiment,extending the range of time involves both initiating transmission of amessage preamble for outgoing signals at a time earlier than an expectedstart time as determined from the locally generated view of currenttime, and discontinuing transmission of the message preamble at a timelater than an expected termination time as determined from the locallygenerated view of current time.

According to a particular embodiment of such a method, extending therange of time involves initiating monitoring for incoming signals at atime earlier than an expected monitoring start time as determined fromthe locally generated view of current time, discontinuing monitoring ofthe incoming signals at a time later than an expected monitoringtermination time as determined from the locally generated view ofcurrent time, initiating transmission of a message preamble for outgoingsignals at a time earlier than an expected transmission start time asdetermined from the locally generated view of current time, anddiscontinuing transmission of the message preamble at a time later thanan expected transmission termination time as determined from the locallygenerated view of current time.

According to yet another particular embodiment, receiving the time valueinvolves receiving a representation of a current time generated by alocal timer of the remote device.

In another embodiment of such a method, determining that the time valuediffers from a locally generated view of current time involves comparingthe received time value to the locally generated view of current time,and determining whether a difference between the received time value andthe locally generated view of current time is at least the establishedamount. In a still more particular embodiment, the difference betweenthe received time value and the locally generated view of current timeis a result of at least a deviation between local clock circuitry andremote clock circuitry of the remote device.

According to yet another embodiment, the method further involvescreating the locally generated view of current time using values from atimer local to a device that receives the time value from the remotedevice.

In accordance with another embodiment, a method is provided thatincludes a client device periodically receiving synchronization messagesoriginating at a remote device, where the synchronization messagesincludes a time value corresponding to the remote device'srepresentation of current time and a synchronization time valuecorresponding to the time at which a prior synchronization occurredbetween the client device and the remote device. If a predeterminednumber of the synchronization messages are received at the client device(e.g., consecutively; some determined percentage; etc.), it monitors forincoming messages from the remote device and transmits outgoing messagesto the remote device when the client device determines that acommunication frequency is active. If the predetermined number of thesynchronization messages are not received at the client device, itmonitors for the incoming messages and transmits the outgoing messagesfrom a time prior to when it determines that the communication frequencyis active and until a time beyond when it determines that thecommunication frequency is active.

According to a more particular embodiment, the method further involvesdetermining whether the predetermined number of the synchronizationmessages are consecutively received. In such case, if the predeterminednumber of the synchronization messages are consecutively received at theclient device, the client device monitors for the incoming messages fromthe remote device and transmits the outgoing messages to the remotedevice when the client device determines that the communicationfrequency is active. If the predetermined number of the synchronizationmessages are not consecutively received at the client device, the clientdevice monitors for the incoming messages and transmits the outgoingmessages from a time prior to when the client device determines that thecommunication frequency is active and until a time beyond when theclient device determines that the communication frequency is active.

According to another particular embodiment, the method further involvesadjusting a local timer at the client device to account for timingdifferences between the client device and the remote device.

In yet another embodiment, the method further involves returning tomonitoring for the incoming messages and transmitting the outgoingmessages when the client device determines that the communicationfrequency is active, when the predetermined number of thesynchronization messages are again consecutively received at the clientdevice.

In accordance with another embodiment of the invention, an apparatus isprovided that includes a local timing module configured to generate alocal representation of current time, and a receiver coupled towirelessly receive a remote device's representation of current time. Aprocessor is configured to compare the local and remote representationsof current time, and in response to determining that the local andremote representations of current time differ by at least apredetermined amount, to extend the range of time in whichcommunications signals with the remote device will be communicated.

According to a more particular embodiment, the apparatus furtherincludes a sleep control module configured to awaken the apparatus forcommunication during the extended range of time in which communicationsignals with the remote device will be communicated.

In accordance with another embodiment of the invention, a system isprovided that includes at least one remote device and at least one localdevice. The remote device includes a remote timing module configured togenerate a remote representation of current time, and a transmitterconfigured to wirelessly transmit a time value indicative of the remoterepresentation of current time. The local device includes a local timingmodule configured to generate a local representation of current time anda receiver coupled to wirelessly receive the time value from the remotedevice. The local device further includes a processor configured tocompare the time value and the local representation of current time, andin response to determining that the time value and the localrepresentation of current time differ by at least a predeterminedamount, extending the range of time in which communications signals withthe remote device will be communicated.

The above summary of the invention is not intended to describe everyembodiment or implementation of the present invention. Rather, attentionis directed to the following figures and description which sets forthrepresentative embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in connection with the embodimentsillustrated in the following diagrams.

FIG. 1 is a diagram generally illustrating a representative manner ofproviding an extended communication window to allow errors ordiscrepancies in synchronization to be removed to enable propercommunication of time-dependent messages;

FIGS. 2A and 2B are flow diagrams illustrating representativeembodiments of methods for coordinating synchronous timing betweendevices in accordance with the invention;

FIGS. 3A and 3B are flow diagrams depicting representative manners inwhich a client device reacts to incoming messages in view of whether theclient device is currently in the extended windowing mode;

FIG. 4A illustrates an exemplary sync period in a frequency hoppingcontext;

FIG. 4B illustrates an example of a portion of a representative syncmessage;

FIG. 5 is a state flow diagram illustrating a representative example ofhow a client device enters and exits the extended windowing mode inaccordance with the present invention;

FIG. 6 illustrates a representative compensation process whereby aclient device iterates to make a compensation factor increasingly moreaccurate in accordance with one embodiment of the invention;

FIG. 7 illustrates representative processing arrangements for acommunicating pair of devices;

FIG. 8 is a block diagram generally illustrating representative HVACelements and devices in which principles of the present invention may beapplied; and

FIGS. 9A-9C depict some representative examples of clients, hosts,groups and systems that may benefit from principles of the invention.

DETAILED DESCRIPTION

In the following description of various exemplary embodiments, referenceis made to the accompanying drawings which form a part hereof, and inwhich is shown by way of illustration various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, as structural and operational changes maybe made without departing from the scope of the present invention.

As will be apparent to those skilled in the art from the descriptionprovided herein, embodiments of the invention may be used in anysituation where synchronization between communicating devices may bedesired or required, such as where messages are communicated wirelesslyvia one or more dedicated frequencies or a sequence(s) of frequencies asin the case of frequency hopping. The invention is also applicable toother channel access methods such as frequency division multiplexing,time division multiplexing, code division multiple access, and/or anyother communication methodology where the timing between communicatingdevices may involve synchronization therebetween.

Generally, the present invention relates to facilitating communicationbetween multiple devices. One aspect of the invention involvescoordinating synchronization timing between multiple devices. In oneembodiment, at least a time value indicative of a remote device's viewof current time is received. Using at least this time value, it can bedetermined that the time value differs from a locally generated view ofcurrent time by at least some established amount. In response, the rangeof time in which communication signals with the remote device will bemonitored and transmitted is extended. Thus, where the remote and localtimers are different by some amount, an extended communication window isutilized at the local device to ensure that it “listens” for incomingmessages and signals (e.g., via a message preamble) outgoing messagesfor an extended time sufficient to account for discrepancies between theremote and local device timers.

More particular embodiments involve communications by way of frequencyhopping techniques. Frequency hopping generally refers to a modulationtechnique where the signal carrier is rapidly switched among manyfrequency channels, where each device involved in the communication isprivy to the frequency hopping sequence in order to know when aparticular communication frequency will become active in the sequence.Using the frequency hopping sequence, transmitting devices can properlyaddress targeted devices, and receiving devices can reject informationfrom neighboring devices that are not within their system but withintheir reception range. In one embodiment, a client device periodicallyreceives synchronization messages originating at a remote device (e.g.,the “host” device), where the synchronization messages includes a timevalue corresponding to the host's representation of current time and asynchronization time value corresponding to the time at which a priorsynchronization occurred between the client and host devices. If apredetermined number of the synchronization messages are, in oneembodiment, consecutively received at the client device, it monitors forincoming messages from the host and transmits outgoing messages to thehost when the client device determines that the relevant communicationfrequency is active. On the other hand, if the predetermined number ofthe synchronization messages are not consecutively received at theclient device, it monitors for incoming messages from the host andtransmits its outgoing messages to the host from a time prior to whenthe client device determines that the communication frequency is activeand until a time beyond when the client device determines that thecommunication frequency is active. In this manner, an extendedcommunication window is utilized at the client device to ensure that it“listens” for incoming messages, and/or signals (e.g., via a messagepreamble) outgoing messages for an extended time sufficient to accountfor discrepancies between the client and host timers, if the client isdeemed “unsynchronized” with the host by way of failing to receive thepredetermined number of consecutive synchronization messages.

Thus, the invention provides, among other things, a manner forsynchronizing actions at multiple devices that operate using their ownlocal clocking mechanisms. For example, battery-powered devices mayenter a sleep or other low power consumption mode during periods ofrelative inactivity, but “awake” at some determined time to exchangeinformation. At least one of the devices (e.g., the “master” device,also referred to herein as the “host” device) is tasked with makinginformation available that coordinates synchronous timing. In oneembodiment, one such information item is the time at which a specificsynchronization will take place, or alternatively had taken place.Another information item is the master view of current time. Using thisinformation, other client devices can calculate when the nextsynchronization will take place. Using the current calculation with itsown timer, each client can compare the locally calculatedsynchronization time against what the host's/master's publishedinformation indicates the next synchronization time to be. The clientscan then employ a dynamic windowing process where they turn on (e.g.,awake) earlier and/or stay on later to account for discrepancies in thesynchronization times. Successive iterations allow the window openingsto be narrowed to conserve as much energy as possible.

More particularly, communicating devices may need to synchronize timingbetween one another to facilitate communication therebetween. Forexample, timing for communications between transmitting and receivingdevices may need to be coordinated to enable communication endpoints tosend and receive data at the same time and/or rate. In serialtransmissions, receiving devices may need to be time synchronized to thetransmitting devices to ensure that the receiver(s) can recognizeinformation in the order that the transmitter(s) sent them, and/or canknow when the information block begins and ends. Additionally, invarious embodiments of the present invention, communicating devices maymaintain time synchronization to enable them to cooperate ontime-dependent operations. For example, time synchronization betweentransmitting and receiving devices may enable anticipated messages to besent and/or received at certain time slots of a shared frequency hoppingsequence.

Synchronous communication may involve clocking mechanisms to synchronizethe signals between the transmitting and receiving devices. Local clocksmay be generated using oscillators that oscillate at a particularnominal frequency. In the case of frequency hopping, the transmittingand receiving devices that share a frequency hopping sequence may eachutilize such an oscillator to generate its respective local clocksignal(s). However, clock signals resulting from each of the oscillatorsof the various devices typically do not generate precisely correspondingclock signals, due to component and environmental variances in each ofthe respective oscillators and/or clock signal generation circuitry. Forexample, temperature differences, component and production imprecisions,effects of component aging and/or other factors may result indifferences in the actual frequency generated by different oscillatorsand their associated clock generation circuits. The deviation due tosuch factors is commonly referred to as drift, which is often expressedin parts per million (PPM). Thus, the drift value for a particularoscillator identifies the number of additional or lacking oscillationsthat occur in the time that the oscillator would normally oscillate onemillion times.

One consequence of local clock differences is that messages communicatedbetween multiple devices may be expected by a receiving device at a timethat is different than the time that the sending device sent themessage. In other words, clocking differences at the communicatingdevices may result in message communication that is not completelysynchronized between the communicating devices. Among other things, thepresent invention provides an extended communication window to accountfor such discrepancies, to enable the devices to properly communicatetime-dependent messages.

In one embodiment, the time-dependent messages may be communicated whena receiving device is prepared to receive the message(s). Moreparticularly, it is typically beneficial to conserve energy consumed byAC or DC powered devices. As an example, the service life betweenbattery replacements can be extended by conserving energy consumption ofbattery powered devices. To conserve power consumption, such devices mayenter a sleep mode or other reduced power mode where power consumptionis reduced until the device is needed, at which time it will “wake up,”or otherwise return to an appropriate operating power. Messages can becommunicated when two or more communicating devices are awake, and thusany of the devices in sleep mode should know when to awake in order toreceive messages or otherwise engage in communicating with otherdevices.

FIG. 1 is a diagram generally illustrating a representative manner ofproviding an extended communication window to allow errors ordiscrepancies in synchronization to be removed, so that time-dependentmessages can be properly communicated. In the embodiment of FIG. 1, itis assumed that a device 100 has undergone a first “synchronization”with another device(s) 102. For example, the device 100 may haverequested information from the other device 102, and the device 102responded with synchronization information. In one embodiment, suchsynchronization information includes the time at which the nextsynchronization will occur, and the device's 102 view of current time.When the device 100 first receives this information from the device 102,the device 100 can be considered synchronized with the device 102.However, each of the communicating devices 100, 102 may have theirrespective clocks/timers running at slightly different speeds asdescribed above. Consequently, by the time that the next synchronizationperiod occurs where the device 102 again provides synchronizationinformation (including the time at which a specific synchronization hadtaken place, and the device's 102 view of current time), the timingbetween the two devices 100, 102 may be slightly off. In accordance withthe invention, an extended communication window can be utilized at thedevice 100. The extended communication window enables the device 100 tolisten for further synchronization messages and other incoming messagesat a point earlier than, and/or for a period longer than, the time thatthe device 100 would have otherwise monitored for a message from thedevice 102. In this manner, the device 100 can account for differencesin timing between the devices 100, 102. Further, the device 100 candetermine the difference in timing between itself and the device 102,and can adjust itself for the next synchronization message.

As shown in FIG. 1, the representative device 100 has its own localtiming 104, and the device 102 has its own local timing 106. In responseto a request by the device 100, or at the device 102's initiative,remote timing information 108 can be provided to the device 100. Thistiming information 108 may include, for example, the time at which asynchronization message will occur, and the device 102's view of currenttime. In one embodiment, the device 102 serves as a host to one or moredevices including device 100, in which case the “host” 102 representsthe master view of current time. Upon first receiving the remote timinginformation 108 from the device 102, the timing of device 100 can beconsidered synchronized with the timing of device 102.

In some cases, the device 100 may expect to receive a message(s) fromthe device 102 at a certain time. For example, synchronization messagesmay be periodically or otherwise sent from the device 102 to the device100 to maintain synchronization between the devices 100, 102. As anotherexample, the device 100 may expect to receive a message, such as aresponse to a request, at a particular time. For example, the device 100may expect to receive a response to an inquiry, and the device 100 willlisten for the response at the time that a certain frequency of afrequency hopping sequence is active. A synchronization offset analysis110 at the device 100 can determine whether the local timing 104 differsfrom the remote timing 108. If the synchronization offset analysismodule 110 determines that the timing between the devices issufficiently synchronized, the devices 100, 102 can be considered to besuitably synchronized and “compensated” as used herein. In this case,the communication window 112 in which the device 100 monitors forincoming messages (e.g. synchronization messages, response messages,etc.) can remain in its normal state. For example, in this case thedevice 110 can begin monitoring for the message(s) from the device 102in a time range determined from its local timing 104. An example in afrequency hopping sequence context may be that the device 100 beginsmonitoring for an expected message when the local timing 104 indicatesthat the relevant message frequency is active, and ends monitoring forthe expected message when the local timing 104 indicates that the activefrequency is ending in favor of the next frequency of the frequencyhopping sequence.

On the other hand, the synchronization offset analysis 110 may concludethat the timing between the devices is not sufficiently synchronized,and is in an “uncompensated” state. In this case, the communicationwindow is extended 114 at one or both ends of the otherwise standardcommunication window 112. In one embodiment, the communication window112 is extended in the uncompensated state by extending the time 118prior to the start of the standard communication window 112, andextending the time 120 following the end of the standard communicationwindow 112. The extended communication segments 118, 120, resulting inthe extended communication window 114, can be applied when the device100 is transmitting or receiving information to or from the other device102. Thus, the extended communication window can apply tosynchronization messages and/or any other messages that may be sentbetween communicating devices. In one embodiment, the communicationwindow may be extended such that communicating devices will awakenand/or sleep commensurate with the extended communication window 114.

In one embodiment, the synchronization offset analysis 110 may beaccomplished by determining that a consecutive number of messagesincluding the remote timing information 108 have been received. In otherembodiments, the analysis may be accomplished by determining that somepercentage of messages including the remote timing information 108 hasbeen received. For example, two out of an expected three receivedmessages indicates that the timing between the communicating devices issufficiently synchronized, or three out of an expected four receivedmessages, etc. The criteria may be a difference between the remotedevice's 102 local timing 106 and the local device's 100 local timing104. Thus, while one embodiment of the invention involves thesynchronization offset analysis 110 monitoring for some consecutivenumber of sync messages being received at the device 100, the inventionis applicable to other criteria for designating the timing of thecommunicating devices as sufficiently synchronized.

As described more fully below, the one or more extensions 118, 120 maybe based on an expected worst case deviation of the local timing 106 andthe local timing 104. For example, this deviation can be determinedbased on quality specifications of the oscillator and/or timingcircuitry associated with the timing modules 104, 106. Where timingcomponents have larger PPM (parts-per-million) deviations, largerwindows 118, 120 can be used. Similarly, where timing components havesmaller PPM deviations, smaller windows 118, 120 can be used.

FIG. 2A is a flow diagram illustrating a representative embodiment of amethod for coordinating synchronous timing between devices in accordancewith the invention. In the illustrated embodiment, each of the devicesinvolved in the communication maintain 200 their own local timers toprovide a respective time value. For each client device, it isdetermined 202 if a scheduled communication time has arisen, calculatedusing the client device's local timer. For example, each client devicemay determine whether it is a determined “wake up” time. If so, theclient device(s) receives synchronization data published 204 orotherwise provided by the master (e.g., host) device, which in oneembodiment is referred to as the host device. As indicated above, thecommunicated synchronization data includes the master (e.g., host) viewof current time and the synchronization time. For example, the masterview of current time refers to what the master's (e.g., host's) localtimers believe the current time to be, and the synchronization timerefers to the time that the next synchronization will occur (or in somecases, when the last synchronization occurred). The client devices thatreceive the synchronization information also have local timers runningthat identify what the respective client believes the current time tobe. The client device(s) compares 206 the master view of current timeand the locally generated time. As shown at block 208, when the resultof the comparison exceeds a threshold amount, the respective clientextends the turn on and/or turn off time. For example, in oneembodiment, the clients that determine the comparison results to exceedthe threshold amount will extend the window for receiving subsequentmessages and extend the window for transmitting subsequent messages. Inone embodiment, if the comparison 206 indicates that the master view ofcurrent time and the client's local time are sufficiently close (i.e.,do not exceed the threshold amount 208), then the windowing feature isnot employed at that time, and the client's local view of current timeis used in determining when to activate its receiving and/ortransmitting functionality.

Where the client entered the extended windowing feature 208, it willremain in this extended windowing mode until some defined events occur,embodiments of which are later described in connection with FIG. 5. Inone embodiment, being in the extended windowing mode causes the clientto extend the time in which it listens for incoming messages from thehost device, and to extend the time in which it transmits messagepreambles when it is attempting to transmit messages to the host device.This can apply to some or all of the messages affecting the clientdevice. For example, in one embodiment, the extended windowing isapplied to any incoming message directed from the host to the client,and to any outgoing message directed to the host. Messages from the hostto the client may be messages to control the client device, to requestinformation from the client device, to provide information to the clientdevice, or any other data that may need to be communicated from a hostdevice to a client device (including synchronization messages). Messagesfrom the client to the host may similarly include status information,control information, requests, or any other data that may need to beprovided to the host. Thus, when in the extended windowing mode, thepresent invention may be applied to all or any subset of messagescommunicated between the relevant communication devices.

FIG. 2B is a flow diagram illustrating a representative embodiment of amethod for coordinating synchronous timing between devices in accordancewith the invention. In the illustrated embodiment, the client devicereceives 210 a synchronization message that includes at least the remotedevice's representation or “view” of current time, as well as asynchronization time value of when a prior synchronization occurred. If,as determined at block 212, a predetermined number of synchronizationmessages were consecutively received, the client will monitor forincoming messages and signal the transmission of outgoing messages at atime determined by the client device as shown at block 214.

If, on the other hand, the predetermined number of synchronizationmessages were not consecutively received by the client device, theclient device will utilize an extended communication window 216 toaccount for timing differences between the devices. For example, whenthe client device is to send a message(s) to the host device, the clientdevice will begin transmitting its outgoing message preamble from a timeprior to the time, and for a duration beyond the time, that the clientotherwise locally determines that the communication frequency is activeas shown at block 216A. In another example, when the client device is tomonitor for an incoming message(s), it will monitor for the message(s)from a time prior to the time, and beyond the time, that the clientdevice otherwise locally determines that the communication frequency isactive as shown at block 216B. In this manner, an extended communicationwindow is utilized at the client device to ensure that it “listens” forincoming messages and signals (e.g., via a message preamble) outgoingmessages for an extended time sufficient to account for discrepanciesbetween the client and host timers, if the client is deemed“unsynchronized” with the host by way of failing to receive thepredetermined number of consecutive synchronization messages.

It should be noted that receipt of consecutive synchronization messagesas described in connection with FIG. 2B is just one example of thecriteria for determining whether to extend the communication window, butconsecutive receipt is not required. For example, receipt of somethreshold percentage of synchronization messages in a time period may beused, or any other desired criteria that is indicative of whether thecommunicating devices are sufficiently synchronized.

FIGS. 3A and 3B are flow diagrams depicting representative manners inwhich a client device reacts to incoming messages in view of whether theclient device is currently in the extended windowing mode. While thehost (master) and client devices may be any devices, for purposes ofthis example it is assumed the devices are part of a heating,ventilation and air conditioning (HVAC) system. Such environmentalcontrol systems may include devices such as thermostats, equipmentinterfaces, sensors, remote controls, zoning panels, dampers,humidifiers, dehumidifiers, etc. It may be beneficial for some or all ofthese devices to communicate with each other wirelessly, whichsignificantly eases installation and wiring complications. Wirelessunits also provide users with flexibility of use, and more options inpositioning the devices. These and other advantages of implementing airinterfaces have led to the use of the wireless transmission of some datain HVAC systems. Representative examples of such HVAC systems aregenerally described below, however it should be recognized that theaforementioned systems, apparatuses and methods may be used in anycommunication device and associated system.

The embodiments of FIGS. 3A and 3B also assume the use of a sharedfrequency hopping sequence, such that the client device will “awake”when the relevant communication frequency arises in the shared frequencyhopping sequence. Thus, at one of the frequencies (which may change) ofthe frequency hopping sequence, the host device will send a message tothe client, and the client will know when, and what frequency, themessage will be sent. In general, frequency hopping is used to theextent that transmissions of information and receptions of communicatedinformation take place according to “sequences” of communicationfrequencies. In one particular embodiment, devices may use a sharedfrequency hopping sequence for receiving messages that is different thana device-specific frequency hopping sequences used to transmit messages.One such system and method is described in co-pending application U.S.patent application Ser. No. 12/253,613, filed on Oct. 17, 2008, havingAttorney Docket Number H0016780 (HWI.047.A1) and entitled “System,Apparatus and Method for Communicating Messages Using Multiple FrequencyHopping Sequences,” the content of which is incorporated herein byreference in its entirety.

The embodiment of FIG. 3A is directed to the transmission of a messagefrom a host device (e.g., zoning panel) to a client device (e.g.,humidifier). The host sends 300 a message to the client, which in theillustrated embodiment is a status request message. It is determined 302whether the client is in the extended windowing mode, which could occurin the manner described in connection with FIG. 2A. If the client is notin the extended windowing mode, the client awakes 304 or otherwisebecomes active for message receipt at the time the relevant frequency ofthe shared frequency hopping sequence arises in the sequence based onthe client's local timing. On the other hand, if the client is in theextended windowing mode, it awakes 306 or otherwise becomes active formessage receipt earlier than, and remains awake/active beyond the endof, the time that the relevant frequency of the shared frequency hoppingsequence serves as the communication frequency. In one embodiment, theprocess of FIG. 3A is used regardless of the type of message received bythe client, such as standard operating messages, synchronizationmessages, etc.

The embodiment of FIG. 3B is directed to the transmission of a messagefrom a client device to a host device. The client determines 310 that itis to transmit a message to the host. It is determined 312 whether theclient is in the extended windowing mode, which could occur in themanner described in connection with FIGS. 2A and/or 2B. If the client isnot in the extended windowing mode, the client begins transmitting thepreamble (or other analogous indication of an ensuing message) at thestart of, and until the end of, the normal time the relevant frequencyof the shared frequency hopping sequence occurs based on the client'slocal timing. If the client is in the extended windowing mode, theclient begins transmitting the message preamble prior to the start of,and beyond the end of, the normal time the relevant frequency of theshared frequency hopping sequence occurs.

It should be noted that FIGS. 3A and 3B depict functional operations,and are not intended to suggest sequential activities. For example,while it may be the case that it is first determined 302 whether theclient device is in extended mode, this may be determined before, afteror concurrently relative to the host sending 300 the status request, andmay be performed, and may also be performed concurrently with theawakening 304/306 of the client device. FIGS. 2A and 2B similarly do notrequire any sequence of flow set forth in the diagram, but rathersuggest functional operations. As an example, the client device may, ormay not, determine 202 the scheduled communication time before themaster device publishes 204 its synchronization data.

As previously indicated, certain events dictate when the client devicewill be in the extended windowing mode. In accordance with oneembodiment, these events focus on if and how often the client devicereceives synchronization messages from the host device during successivesync periods. Before describing an example of the conditions used todetermine if and when a device will enter or remain in the extendedwindowing mode, an exemplary sync period in a frequency hopping contextis described in connection with FIG. 4A.

In a frequency hopping context, a plurality of frequencies are orderedinto a frequency hopping sequence. For example, in a frequency hoppingsequence having fifty frequencies, the frequencies F₀-F₄₉ may berearranged into any order of the fifty frequencies. This sequence of,for example, fifty frequencies repeats itself over and over, while boththe host(s) and client(s) monitor the passage of time to know whichfrequency is active for communication at a particular time. Every sooften, a sync period is injected into the repeating frequency hoppingsequence to facilitate synchronization of the communicating devices inaccordance with the invention.

In FIG. 4A, segment 400A represents a first repeating sequence offrequencies, referred to herein as a “frequency sequence period.” Atsome determined interval, such as every fifteen seconds, asynchronization (sync) period 402A occurs, which is described more fullybelow. After the intervening sync period 402A, the frequency hoppingsequence resumes as shown in segment 400B, followed again by a syncperiod 402B, and so on. In one representative example, a sync periodoccurs every 112 frequency sequence periods plus one frequency period,although any desired periodic or non-periodic manner of providingsynchronization messages may be utilized. Using, for example, a 1/4096timer resolution example, this results in a sync period occurringapproximately every fifteen seconds (approximately 61,000 ticks 15seconds). The exemplary sync period is divided into four equal syncmessage periods 404, 406, 408, 410, each 22 frequency periods long (242ticks). In one embodiment, the frequencies used during eachsynchronization message period are in order of the first four frequencyperiods in the sync period. For example, if the first four frequenciesof the sync period are F₄₀, F₁₄, F₄₇ and F₃₈, then each of the four syncmessage periods 404, 406, 408, 410 will respectively use frequenciesF₄₀, F₁₄, F₄₇ and F₃₈. In the illustrated embodiment, the entire syncperiod is 88 normal frequency periods (e.g., 236 mSec).

Each of the clients operating in the system wake up to hear the syncmessage in one embodiment. When a client hears a sync message such assync message 406, it may ignore the remaining sync messages 408, 410 inthat sync period 402A. As previously indicated, each of the syncmessages 404, 406, 408, 410 contain the host's 24-bit timer value at thetime of the start of the current sync message period (i.e., the masteror “host” view of current time), as well as the host's timer value atthe start of the last frequency sequence.

An example of a portion of a sync message 404 from FIG. 4A is shown inFIG. 4B. The sync message 404 may include a preamble 404A and variousaddresses such as the network address 404B, destination address 404C andsource address 404D. As indicated above, the sync message 404 alsoincludes synchronization information 420. One part of the information420 is the master view of current time depicted as the synchronizationmessage time stamp 404E taken at a particular host transmit time.Another part of the information is the host's timer value relative tothe start of a frequency sequence. This may represent the host's timervalue at the start of the last frequency sequence, or alternatively thenext scheduled synchronization message time 404F based on the host'stimer. This representative synchronization message 404 may end with acyclic redundancy check 404G.

As indicated above, the sync message 404 may include varioussynchronization information, such as the master view of current time;time at the start of a frequency hopping sequence, etc. In oneembodiment involving frequency hopping, there are three relevant timesof which the synchronization message can provide; 1) the actual timestamp for the message that is going out; 2) the time stamp of thebeginning of the most recent synchronization period; 3) the time stampof the beginning of the most recent frequency sequence.

It should be recognized that the representative number and durations ofsync period 402A shown in FIG. 4A are merely for purposes of example. Asit pertains to the invention, the more relevant aspect is thatsynchronization information, such as the host's view of current time andthe host's view of the next (or last) synchronization message time, isprovided to the clients. Using such information, the clients can staysynchronized by enabling the clients to know when to begin/end listeningfor incoming messages and/or begin/end transmitting outgoing messages.Thus, in accordance with embodiments of the invention, the receipt ofthe synchronization information enables the clients to determine whetherto enter the extended windowing mode in order to maintainsynchronization between devices that are to communicate with oneanother.

As previously indicated, when the client is in the extended windowingmode (e.g., block 208 of FIG. 2A) in accordance with one embodiment ofthe invention, it will remain in this extended windowing mode until oneor more defined events occur. FIG. 5 is a state flow diagramillustrating a representative example of how a client device enters andexits the extended windowing mode in accordance with the presentinvention. The following description sets forth one particularembodiment for doing so, for purposes of facilitating an understandingof this aspect of the invention. However, those skilled in the art willreadily appreciate that this aspect of the invention is equallyapplicable to other desired design parameters.

In this representative embodiment described in connection with FIG. 5,it is assumed that each of the client devices implements a hardwaretimer with 1/4096 second resolution, although any selected resolutionmay be implemented according to the particular design. One embodimentinvolves each client device remaining within one timer tick count of itsmaster/host. For example, where the host and client communicate using acommon frequency hopping sequence, the host and client timers may needto remain within one clock period or “tick” of one another so that bothdevices are communicating on the same frequency at the substantially thesame time.

In order to maintain such a timing relationship between communicatingdevices, one device such as the host may send one or moresynchronization messages to client devices in a dedicated block of timereferred to herein as a synchronization (or sync) period. In oneparticular embodiment, the host transmits four synchronization messagesin the sync period as was also illustrated in connection with FIG. 4A.Issuing multiple synchronization messages in each sync period increasesthe chance of client devices perceiving one of the synchronizationmessages.

The sync period may be designed to occur as often as desired, and in oneembodiment occurs approximately every 61,000 clock ticks (15 seconds)based on a 1/4096 second resolution timer. When a client recognizes oneof the synchronization messages, it may ignore the remainingsynchronization messages in the sync period. However, in one embodiment,clients may still operate correctly even if they miss all the syncmessages in 2 consecutive sync periods. In an embodiment requiring eachclient device to stay within one timer tick count of its host, eachclient must maintain+/−one timer tick accuracy for approximately 45seconds (approximately 15 seconds times three sync periods).

For purposes of illustration, assume client hardware timers with 1/4096second resolution that utilize crystal oscillators having −50, +130parts per million (PPM) accuracy over the operating temperature range.Assuming the foregoing, after three sync periods (approximately 45seconds), the most that any of the timers should deviate is shown in therepresentative example equation below:

((50+130)/10⁶)*3*61611)=+/−33 ticks  (EQUATION 1)

As indicated above, design parameters may suggest or require that thehost and client timers be within some established number of clock ticks,such as one clock tick in the above representative example.

Where the host and client timers are to remain within one clock tick ofone another, one embodiment involves each of the client devicesadjusting for the difference between its timer and its respective host'stimer. This can be done, for example, by calculating a compensationfactor using information from at least two synchronization messages.With each synchronization message received thereafter, the client caniterate to make the compensation factor increasingly more accurate.

Each client initially becomes associated with a master, also referred toherein as a host. In one embodiment, a client becomes associated withits host through an enrollment or “binding” process. An enrollmentprocess enables the enrolling device(s) to be made known to the host,and vice-versa. For example, devices that are known to be in the samesystem may be allowed to communicate with one another, relative to otherdevices that have not (or are not suppose to) enroll with the host. Moreparticularly, devices in a system, and especially systems involving oneor more wireless devices, may join or leave the system or network ofdevices at various times. One time is during initial installation, wheresome or all of the devices may undergo such an enrollment or bindingprocess which allows devices to learn about each other so they cancooperate, such as communicate with one another, obtain authorization tocommunicate with one another, etc. Other devices may join the systemafter initial installation, such as when a new device is installed inthe system, at which time this new device(s) can be enrolled in thesystem. In the context of wireless devices, devices may need to gainknowledge of the address(es) of other wireless devices that they cancommunicate with. This address or other information allows sendingdevices to address intended recipient devices correctly, and allowsreceiving devices to reject information from neighboring devices thatare within the wireless communication range but not part of theparticular system. Devices can be made aware of each other, andconsequently each other's address, through a process of “binding” whereinformation particular to each device is exchanged. A bound set ofcommunication devices know the particular information of the otherdevices, and know which devices from which it should accept messages.This binding process is described for purposes of illustration only, asany desired enrollment or binding process may be utilized in connectionwith the present invention.

A client's initial synchronization message is typically received outsideof the sync period when the client enrolls, and if/when it later losessynchronization and must regain it. An inaccurate compensation factorwill result if the duration between synchronization messages is toosmall. Therefore, in one embodiment, the client does not use the initialsynchronization message in the compensation calculation, and whensynchronized it ignores any synchronization messages that are not in async period. In such an embodiment, this guarantees at least 15 secondsbetween synchronization messages.

In accordance with one embodiment of the invention, a client device maybe in one of three states, including 1) unsynchronized; 2) synchronizedbut uncompensated; and 3) synchronized and compensated. An example ofthis embodiment is provided in FIG. 5, which depicts a state diagram ofthree exemplary synchronization states and associated actions.

A first state for a client device(s) is shown as the unsynchronized 500state. A client device will typically be unsynchronized in its “out ofthe box” condition; i.e., prior to its enrollment to the system. Thedevice may also be unsynchronized at other times, such as when it isbeing replaced by a replacement device, when it specifically queries forsynchronization, battery replacement or other power loss/interruption,or when it otherwise loses its synchronization with its host.

When the device is in the unsynchronized state 500, it will at somepoint receive 502 a synchronization message during a sync period. In oneembodiment, this first synchronization message is not used in theensuing compensation calculation, as described more fully below. Theclient device will request synchronization information from the host orotherwise receive such synchronization information from the host. Thesynchronization information provided in the synchronization message 502may include, for example, the time at which a synchronization will take(or had taken) place, and the host's view of current time. When theclient receives this information, its local timer will begin timing forthe next synchronization, and the client/host will at least temporarilybe deemed synchronized, but “uncompensated.” It is assumed to beuncompensated (but not necessarily so) because the client and hostdevices have separate timers operating, which may operate at slightlydifferent speeds due at least to the potential PPM accuracy deviations.When the client device is in this state, the extended windowing mode isapplied in accordance with the present invention.

When a client device is in the synchronized but uncompensated state 504,it might not meet the accuracy requirement of being within +/−1 tick ofthe host, and may be as much as +/−33 ticks off, based on the −50, +130PPM accuracy example described above. Communications between the hostand client may still occur, but in accordance with the invention theclient can adjust its timing for the possible inaccuracies that mayresult in less efficient use of power and bandwidth. Assuming the −50,+130 PPM accuracy example, while a client is in the synchronized butuncompensated state, the client will turn on its receiver or otherwisebegin monitoring for incoming messages at least 33 ticks earlier than itnormally would, and will leave its receiver on or otherwise continuelistening at least 33 ticks longer than it normally would. The extendedlistening window is thus 33 ticks at each of the beginning and end ofthe time the local timer in the client device suggests the messagereceipt time to be. As will be readily apparent to those skilled in theart, the actual extended window in which the client will listen dependson the calculation in Equation 1.

As an example, assume the client device will awake to listen for anyincoming messages when a frequency in its receiver frequency hoppingsequence reaches the same frequency in which the host device willtransmit a message to the client. Also assume that the “extended window”is 33 ticks prior to and another 33 ticks following the duration thatthe relevant frequency of the frequency hopping sequence is calculatedto be active in the client device based on the client device's localtimer. While in the synchronized but uncompensated state 504, the clientdevice will turn on its receiver at least 33 ticks early using the samefrequency that it would use at the normal time, and will leave itsreceiver on at that same frequency at least 33 ticks longer than itnormally would. In this manner, the client will be listening for aduration that accounts for the potential deviation between the clientand transmitting host's respective timers.

In one embodiment, the extended window process is also applied tomessages transmitted from the client. Particularly, the preamble inclient-sent messages will start at least 33 ticks early, and will end atleast 33 ticks later, than the normal duration of the preamble based onwhat is directed by the client's own local timer. As an example, againassume the same PPM accuracy, and that the implementation involves oneor more frequency hopping sequences. In this example, the preamble inall client sent messages whose start time is determined by the host'shop sequence will start at least 33 ticks early using the same frequencythat it would use at the normal time, and the preamble in all clientsent messages whose start time is determined by the host's hop sequencewill end at least 33 ticks later than when it normally would. In yetanother particular embodiment, the requirement of extending the preamblein connection with client-sent messages takes priority over extendingthe listening window for received messages.

In another embodiment, a guard band is implemented, which ensures that aclient does not start sending a message if it would extend into the syncperiod. In accordance with one embodiment of the invention, the extendedwindow impacts the determination of whether a message can be initiatedby a client in view of the guard band. For example, the client's guardband is extended to be 33 ticks (using the previous example) earlierthan, and 33 ticks later than, it normally would. In yet anotherparticular embodiment, the requirement of extending the window for theguard band takes priority over the requirements of extending thepreamble in connection with client-sent messages and extending thelistening window for received messages.

The particular client device will remain in the synchronized butuncompensated state 504, while applying the dynamic extended windowingprocess in accordance with the invention, until the client devicequalifies to enter the “synchronized and compensated” state 506, orreturns to an “unsynchronized” state 500. In one embodiment, the devicemay return to the unsynchronized state 500 in any one of a plurality ofmanners. For example, if the client device encounters three consecutivesync periods without receiving a sync message as shown at block 508, itis returned to the unsynchronized state 500 where the client will againrequest or otherwise receive a sync message and will start the processanew. The number “three” sync periods may differ in different designs,and is set to three in the present example based on the exemplary PPMaccuracy of the oscillators, the representative requirement that thedevice stay within one tick count of its host, and that the client maystill operate correctly even if it misses all the sync messages in 2consecutive sync periods. Other examples in which the device may returnto the unsynchronized state 500 include the device transmitting a queryfor synchronization as shown at block 510, and/or the device unenrolling512 from its host.

If the particular client device receives 514 three or more consecutivesynchronization messages in the present example, excluding the firstsynchronization message 502 received when originally in theunsynchronized state 500, it will be considered to be “synchronized” andenters the synchronized and compensated state 506. In this state, theextended windowing process described in connection with the synchronizedbut uncompensated state 504 is discontinued. In other words, the clientdevice will not monitor for incoming messages earlier and later than itslocal timer suggests, it will not begin transmitting its preambleearlier and continuing the preamble transmission beyond what its localtimer suggests when transmitting messages, and it will not extend theguard band beyond what its local timer suggests. Thus, in theillustrated embodiment, the client device implements the extendedwindowing process while in the synchronized but uncompensated state 504,and does not extend its normal listening/transmitting durations while inthe synchronized and compensated state 506. Among other things, thisenables the client device to save energy, which is particularlybeneficial for battery-operated client devices.

The client device remains in the synchronized and compensated state 506until the device unenrolls 516, sends a query for synchronization 518,or until three (in the present example) consecutive sync periods occurwithout receiving a synchronization message 520. If any of these events516, 518, 520 and/or other established events occur, the device returnsto the unsynchronized state 500 where the process starts anew.

As indicated above, one embodiment involves maintaining the host andclient timers within some established time relative to one another, suchas within one clock tick of each other. The client devices may adjustfor the difference between its timer and its respective host's timer by,for example, calculating a compensation factor using information from atleast two synchronization messages. With each synchronization messagereceived thereafter, the client can iterate to make the compensationfactor increasingly more accurate. A representative compensation processis described below, and in connection with FIG. 6. It should berecognized that the example of FIG. 6 is provided for purposes offacilitating an understanding of how such a compensation algorithm mayallow a client device 600 to adjust for the difference between its localtimer 602 and the timer 604 of its host 606, however other compensationalgorithms may be analogously implemented.

In this example, client time is represented as a 24-bit value 608, usingan 8-bit variable 610 for the most significant bits (MSBs) and a 16-bithardware timer 612 with 1/4096 second resolution for the leastsignificant bits (LSBs). At least the hardware timer 612 receives clockpulses/ticks from its oscillator (OSC) 614. Each overflow of thehardware timer 612 (approximately every 16 seconds in the presentexample) generates an interrupt 616 that increments the 8-bit variable610. The hardware timer 612 utilizes several compare registers 618 thatgenerates interrupts 616 at particular times, up to approximately 16seconds in the future. When a synchronization message 620 is receivedfrom the host's 606 synchronization message module 622, the 24-bit time608 in the client 600 could be changed to match the host's timer 604.However this would involve changing the hardware timer value 612, andwhen that is changed, any compare values that had previously been setbecome invalid. Instead of adding special software to also change thecompare values, the hardware timer value 612 need not be changed inembodiments of the present invention. Rather, the client device's timer602 continues to run unmodified when synchronization occurs, whereby theclient 600 refers to any future time in terms of the host's time 604,and performs a hardware, firmware and/or software calculation 624 toconvert host time 604 to its own time 608 in order to set its timercompare registers.

In one embodiment, when a client receives a sync message, it does notmake adjustments to an existing compare register; however it uses thenew information to set any new compare registers. As long as thecompensated timer error at the start of the previous sync period waswithin 1 tick, any compare registers settings are still valid after anew sync period. After the transition from the “Unsynchronized” state500 (FIG. 5) to the “Synchronized but Uncompensated” state 504 (FIG. 5),the device is accurate to within one tick after two more sync periods,however the compare register may be inaccurate. This is why, in oneembodiment, the client does not transition to the “Synchronized andCompensated” state until it gets the third sync period 514 (FIG. 5).

The functions associated with the present invention may be performed bydiscrete circuitry and/or computing system hardware. In one embodiment,the devices that will communicate with one another utilize aprocessor(s), CPU(s), computer(s), or other processing system to performthe stated functions. Accordingly, hardware, firmware, software or anycombination thereof may be used to perform the various functions andoperations described herein.

Representative processing arrangements for a communicating pair ofdevices 700, 750 is illustrated in FIG. 7. The device 700 represents anytransmitting device capable of performing the communication functionspreviously described, such as sending a message to or receiving amessage from another device 750. A device may be both a transmitting andreceiving device, and a device referred to herein as a transmitting orreceiving device is based on whether it is operating as a transmitter orreceiver for purposes of that description. In the illustratedembodiment, the device 700 represents a client device that is capable ofcommunicating over the air, such as by radio frequency (RF)communications. By way of example and not of limitation, the device 700may represent communication portions of a thermostat, sensor, remotecontrol, damper, humidifier, dehumidifier, etc.

The representative device 700 implements computing/processing systems tocontrol and manage the conventional device activity as well as thedevice functionality provided by the present invention. For example, therepresentative device 700 includes a processing/control unit 710, suchas a microprocessor, controller, reduced instruction set computer(RISC), central processing module, etc. The processing unit 710 need notbe a single device, and may include one or more processors. For example,the processing unit may include a master processor and one or moreassociated slave processors coupled to communicate with the masterprocessor.

The processing unit 710 controls the basic functions of the device 700as dictated by programs available in the program storage/memory 712. Thestorage/memory 712 may include an operating system and/or variousprogram and data modules associated with the present invention. In oneembodiment of the invention, the programs are stored in non-volatilestorage/memory so that the programs are not lost upon power down of thedevice. The storage 712 may also represent one or more of other types ofread-only memory (ROM) and programmable and/or erasable ROM, randomaccess memory (RAM), subscriber interface module (SIM), wirelessinterface module (WIM), smart card, or other fixed or removable memorydevice/media. The storage 712 may also include removable media 714 (e.g.disk, CD-ROM, DVD, etc.) that can be read via the appropriate interfacesand/or by appropriate media drives. The relevant software for carryingout device operations may be provided to the device 700 via any suchstorage media, or may be transmitted to the device 700 via data signalssuch as by way of a network.

For performing other device functions, the processor 710 may be coupledto user input interface 718 associated with the device 700. The userinput interface 718 may include, for example, a keypad, functionbuttons, joystick, scrolling mechanism (e.g., mouse, trackball), touchpad/screen, and/or other user entry mechanisms. A user interface (UI)720 may be provided, which allows the user of the device 700 to perceiveinformation visually, audibly, through touch, etc. For example, adisplay 720A and/or speaker 720B may be associated with the device 700.Other user interface (UI) mechanisms 720C can also or alternatively beprovided.

The processor 710 is also coupled to a transceiver 724, which representseither a transceiver or discrete transmitter and receiver components.The transceiver 724 is configured to communicate RF signals, includingcommunicating RF signals using frequency hopping as described herein.The transceiver 724 is coupled to an antenna 726.

In one embodiment, the storage/memory 712 stores the various clientprograms and data used in connection with the present invention. Forexample, a transmit frequency determination module 730 can be providedfor a transmitting device to identify the frequency at which it willnext transmit a message. A timing module 732 may determine when the nexttransmission frequency becomes active in the relevant frequency hoppingsequence, and/or perform other timing functions such as those associatedwith the timing module 114 of FIG. 1. One or more frequency hoppingsequences 734 as described herein may be stored in the storage 712, asmay other data such as the frequency 736 at which a message was sent sothat the same frequency can be monitored for incoming acknowledgementsignals, responses, etc. In some embodiments the stored frequency(s) 736may also store the last frequency used by the device 700 to transmit orreceive a message, so that the next frequency in the frequency hoppingsequence may be used to send or receive a subsequent message.

The storage may also store program modules to enable the device 700 toperform other functions in accordance with the invention. For example,the storage/memory 712 may include a message creation module 738 thatformulates a query or other message for transmission to a host or othertarget device 750. A sleep control module 740 controls functional unitsand/or other components of the device 700 in order to at least conservepower consumption. For example, the sleep control module 740 may beconfigured to turn off the transceiver 724 or the transmitting orreceiving portions thereof. The sleep control module 740 can beconfigured to reduce or temporarily suspend any other desired functionaloperation and/or component of the device 700 to conserve localresources.

Still other modules may include an acknowledge module 742, which canrecognize acknowledgement signals from another device 750, and/or createacknowledgement signals to return to another device 750 to notify itthat a response or other message has been received. For example, theacknowledge module 742 can recognize receipt of an acknowledgementsignal from another device by, for example, parsing a received messageand determining from header information and/or the message body that itis an acknowledgement signal for the transmitted message. In anotherparticular embodiment, the acknowledge module 742 can formulate theheader information and message body to create an acknowledgement messageto be transmitted to the responding device 750 to notify the respondingdevice 750 that the device 700 received a message (i.e. responsemessage) in response to an inquiry or other message.

These and other modules may be separate modules operable with theprocessor 710, may be a single module performing each of thesefunctions, or may include a plurality of such modules performing thevarious functions. While the modules are shown as multiplesoftware/firmware modules, they may or may not reside in the samesoftware/firmware program. It should also be recognized that one or moreof these functions may be performed using discrete hardware. Thesemodules are representative of the types of functional modules that maybe associated with a device in accordance with the invention, and arenot intended to represent an exhaustive list. Also, other describedfunctions not specifically shown may be implemented by the processor710.

FIG. 7 also depicts a representative receiving device 750 that is thetargeted device of a message sent from the device 700, or the source ofa message directed to the device 700. In one embodiment, the targetdevice 750 represents the communication portions of a host device, suchas thermostats, equipment interfaces, zoning panels, etc. Theillustrated device 750 includes circuitry analogous to that of device700, and similarly includes a processor 752 and storage/memory 754. Inaccordance with one embodiment, the storage/memory 754 and/or mediadevices 756 store the various programs and data used in connection withthe invention. For example, the storage 754 may include a receive timingmodule 760 that is configured to determine when a frequency in itsshared frequency hopping sequence is active; i.e. what frequency isbeing listened to, and when. Stated alternatively, the receive timingmodule 760 identifies an active frequency in the frequency hoppingsequence (shared with the device 700) in which to monitor for incomingmessages. The storage 754 can store at least a receiver frequencyhopping sequence 762, although it may also store a transmitter frequencyhopping sequence (not shown) if it is also a transmitting device. Thedevice 750 may also include other modules, such as a response creationmodule 764 that formulates a response message to respond to a query orother message from an initiating device 700. For example, if the device700 transmits a query to the host 750 to receive a synchronizationmessage, the response creation module can formulate the appropriatesynchronization message, analogous to the sync message module 622described in connection with FIG. 6.

The device 750 may also include other components or modules forperforming other device functions, such as a user input interface 770.The user input interface 770 may include, for example, a keypad,function buttons, joystick, scrolling mechanism (e.g., mouse,trackball), touch pad/screen, and/or other user entry mechanisms. Othercomponents may include a user interface (UI) 772, which allows the userof the device 750 to perceive information visually, audibly, throughtouch, etc. For example, a display 772A and/or speaker 772B may beassociated with the device 750. Other user interface (UI) mechanisms772C can also or alternatively be provided. The illustrated processor752 is also coupled to a transceiver 774 (which may represent discretetransmitter and/or receiver components) configured to transmit andreceive RF signals using frequency hopping as described herein. Thetransceiver 774 is coupled to an antenna 776.

The devices 700, 750 may be powered in any desired fashion. In oneembodiment, the device 700 is battery 748 powered, and the sleep controlmodule 740 controls components such as the transceiver 724 in order toconserve power and increase the useable life of the battery 748. Thedevice 750 is not battery powered in the illustrated embodiment, butrather is powered by an external source such as an AC power source 780or DC power source 782.

The functions described in connection with the invention may be used inany device in which data is to be communicated. In one embodiment, thesystems, apparatuses and methods of the invention are implemented inenvironmental monitoring and control systems, such as HVAC systems.Representative examples of such systems are generally described below.However, it should be recognized that the aforementioned systems,apparatuses and methods may be used in any communication device andassociated system.

Environmental control systems can monitor and control numerousenvironmental and safety devices. These devices include, for example,thermostats, HVAC modules, equipment interfaces, sensors, remotecontrols, zoning panels, dampers, humidifiers and dehumidifiers, etc. Itmay be beneficial for some or all of these devices to communicate witheach other wirelessly, which significantly eases installation and wiringcomplications. Wireless units also provide users with flexibility ofuse, and more options in positioning the devices. These and otheradvantages of implementing air interfaces have led to the use of thewireless transmission of some data in HVAC systems.

FIG. 8 is a block diagram generally illustrating representative HVACelements and devices in which air interfaces may be used. FIG. 8 depictsone or more user control units 800, such as wireless thermostats whereusers can enter a temperature setpoint designating a desiredtemperature. Other examples of user control units 800 include humiditycontrol units, lighting control units, security control units, etc.Climate or environmental systems 802 may include the equipment to causethe desired action to occur. One such system 802 is an HVAC system,which includes equipment to raise or lower temperature, humidity, etc.User control units 800 may communicate directly with suchclimate/environmental systems 802, and/or may communicate via one ormore interfaces or zone controllers 804. Remote user control units 806provide portable user control, such as providing a visual and/or audiointerface to the user, and allowing the user to change environmentalsetpoints, check status, etc. Sensors 808 may be used to senseenvironmental conditions, and may be discrete devices (e.g. outdoorair/temperature sensor) or may be integrated into user control units800. Flow and other control equipment 810 may also be used, such asdampers, ultraviolet air treatment lamps, etc. Any of these devices mayneed to communicate information amongst themselves and/or with otherdevices 812, in which the present invention may be utilized.

When these devices communicate wirelessly with one another via radiofrequency (RF) or other wireless means, there is a reasonable chancethat a wirelessly communicating device may experience interference fromneighboring systems or other devices of the same system. Using frequencyhopping can significantly reduce such interference. Communicating viafrequency hopping sequences as described herein enables, among otherthings, multiple devices to communicate in an orderly fashion whileaddressing interference issues.

Some devices in the system may be powered by power sources andcommunicate via wire and/or over the air, while other devices may bebattery-powered and communicate information wirelessly. In oneembodiment, devices that are powered by power sources, such as 24 voltsAC (VAC), may be referred to herein as hosts, and may remain powered onwhile operating in the system. Other devices that are powered by batterymay be referred to herein as clients, and may enter a sleep mode topreserve battery life. A collection of devices including a host(s) andits clients may be referred to as a group, and a collection of physicalgroups that communicate through their host(s) may be referred to as asystem. However, a system as otherwise used herein does not require anysuch groupings, and may involve as few as two communicating devices.

FIGS. 9A-9C depict some representative examples of clients, hosts,groups and systems that may benefit from principles of the invention.Like reference numbers are used for analogous devices where appropriatein FIGS. 9A-9C. Each of the devices depicted in FIGS. 9A-9C may bepowered in any desired manner, such as via an AC power source, batteryor other DC power source, employing energy harvesting such as solarcells, etc. Thus, the examples below that reference possible powersources for various devices are merely representative embodiments forpurposes of illustration.

FIG. 9A illustrates one system 900 where one or more thermostats 902A,902B are configured as hosts, and may be powered by an AC power source,DC source or other power source. Each thermostat 902A, 902B may be wiredto other equipment such as humidifiers 904A, 904B, dehumidifiers 906A,906B, and HVAC equipment 908A, 908B respectively. Battery poweredclients in the embodiment of FIG. 9A include one or more sensors 910,such as an outdoor air sensor (OAS), and one or more remote userinterfaces (RUI) 912 which provide users with remote access and controlof environmental conditions in the system 900. In accordance with oneembodiment of the invention, clients such as the RUI 912 can receivesynchronization messages from a host device such as the thermostat 902Aor 902B.

FIG. 9B illustrates another exemplary system 920 where one or morethermostats 903A, 903B are configured as clients, and may be powered bybatteries. Each thermostat 903A, 903B respectively communicateswirelessly with an equipment interface module (EIM) 922A, 922B that maybe AC-powered and wired to respective HVAC equipment 908A, 908B. In thisembodiment, each EIM 922A, 922B operates as a host and communicates withvarious clients. For example, host EIM 922A can communicate wirelesslywith clients including the thermostat 903A, the sensor(s) 910, and theRUI(s) 912. Similarly host EIM 922B can communicate wirelessly withclients including the thermostat 903B, the sensor(s) 910, and the RUI(s)912. In accordance with the invention, clients such as the thermostat903A can receive synchronization messages from a host device such as theEIM 922A.

FIG. 9C illustrates another system 930 which utilizes area zoning usinga zoning panel 932. In this embodiment, the zoning panel 932 serves as ahost that may be AC-powered. The zoning panel 932 of FIG. 9C isconnected to other equipment such as the HVAC 908A and dampers 934.Clients include the thermostats 903A, 903B, 903C, sensor(s) 910, RUI912, and possibly dampers 934 when such dampers are wirelesslycontrolled. In accordance with the invention, clients such as any of thethermostats 903A/B/C can receive synchronization messages from a hostsuch as the zoning panel 932.

It should be noted that the exemplary environments described in FIGS. 8and 9A-9C are provided merely for purposes of facilitating anunderstanding of representative systems in which the principles of thepresent invention may be employed. From the description provided herein,one skilled in the art can readily appreciate that the invention may beemployed in any system of two or more communicating devices.

Using the description provided herein, the invention may be implementedas a machine, process, or article of manufacture by using standardprogramming and/or engineering techniques to produce programmingsoftware, firmware, hardware or any combination thereof.

Any resulting program(s), having computer-readable program code, may beembodied on one or more computer-usable media such as resident memorydevices, smart cards or other removable memory devices, or transmittingdevices, thereby making a computer program product or article ofmanufacture according to the invention. As such, terms such as “modules”and the like as used herein are intended to include aprocessor-executable program that exists permanently or temporarily onany computer-usable medium or in any transmitting medium which transmitssuch a program. Such “modules” may also be implemented using discretecircuits.

As indicated above, memory/storage devices include, but are not limitedto, disks, optical disks, removable memory devices such as smart cards,SIMs, WIMs, semiconductor memories such as RAM, ROM, PROMS, etc.Transmitting mediums in which programs can be provided include, but arenot limited to, transmissions via wireless/radio wave communicationnetworks, the Internet, intranets, telephone/modem-based networkcommunication, hard-wired/cabled communication network, satellitecommunication, and other stationary or mobile networksystems/communication links.

The foregoing description of exemplary embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not with this detailed description, but rather determined inview of what would be apparent to those skilled in the art from thedescription provided herein and the claims appended hereto.

What is claimed is:
 1. A method comprising: determining if a currentview of time of a remote device differs from a current view of time of alocal device by at least an established amount; in response todetermining that the current view of time of the remote device does notdiffer from the current view of time of the local device by at least theestablished amount, using a non-extended communication window duringwhich communications signals can be communicated between the remotedevice and the local device; and in response to determining that thecurrent view of time of the remote device does differ from the currentview of time of the local device by at least the established amount,using an extended communication window during which communicationssignals can be communicated between the remote device and the localdevice, wherein the extended communication window has a longer durationthan the non-extended communication window.
 2. The method of claim 1,wherein the extended communication window entirely overlaps thenon-extended communication window.
 3. The method of claim 2, wherein theextended communication window starts before the non-extendedcommunication window.
 4. The method of claim 2, wherein the extendedcommunication window ends after the non-extended communication window.5. The method of claim 2, wherein the extended communication windowstarts before and ends after the non-extended communication window. 6.The method of claim 1, wherein the current view of time of the remotedevice is maintained by a timer of the remote device, and the currentview of time of the local device is maintained by a timer of the localdevice.
 7. The method of claim 1, wherein the local devices determinesthat the current view of time of the remote device differs from thecurrent view of time of the local device by at least the establishedamount by comparing timer values from the timer of the remote device andthe timer of the local device.
 8. The method of claim 1, wherein thelocal devices determines that the current view of time of the remotedevice differs from the current view of time of the local device by atleast the established amount by: receiving a time value from the remotedevice; comparing the received time value from the remote device to alocal time value, and determining whether a difference between thereceived time value and the local time value is at least the establishedamount.
 9. The method of claim 1, wherein the local devices determinesthat the current view of time of the remote device differs from thecurrent view of time of the local device by at least the establishedamount by determining that less than a threshold number of expectedmessages were received when using the non-extended communication window.10. The method of claim 1, wherein in response to determining that thecurrent view of time of the remote device does differ from the currentview of time of the local device by at least the established amount,using subsequent communications signals communicated during the extendedcommunication window to calibrate the current view of time of the localdevice with the current view of time of the remote device.
 11. Themethod of claim 10, wherein after calibrating the current view of timeof the local device with the current view of time of the remote device,returning to using the non-extended communication window during whichcommunications signals can be communicated between the remote device andthe local device.
 12. The method of claim 1, wherein when using theextended communication window, the local device: initiating monitoringfor incoming signals from the remote device at a time earlier than thenon-extended communication window would begin; discontinuing monitoringfor incoming signals from the remote device at a time later than thenon-extended communication window would end; initiating transmission ofa message preamble for outgoing signals to the remote device at a timeearlier than the non-extended communication window would begin; anddiscontinuing transmission of the message preamble to the remote deviceat a time later than the non-extended communication window would end.13. A method comprising: repeatedly sending from a remote devicesynchronization messages; if a predetermined ratio of thesynchronization messages are received at the local device, monitoring atthe local device for incoming messages from the remote device andtransmitting outgoing messages from the local device to the remotedevice during a non-extended communication window having a first windowduration; and if the predetermined ratio of the synchronization messagesare not received at the local device, monitoring at the local device forincoming messages from the remote device and transmitting outgoingmessages from the local device to the remote device during an extendedcommunication window having a second window duration, wherein the secondwindow duration is longer than the first window duration.
 14. The methodof claim 13, wherein the synchronization messages including a time valuecorresponding to the remote device's representation of current time anda synchronization time value corresponding to the time at which aprevious or next synchronization message was or will be sent by theremote device.
 15. The method of claim 13, wherein the extendedcommunication window entirely overlaps the non-extended communicationwindow.
 16. The method of claim 15, wherein the extended communicationwindow starts before the non-extended communication window.
 17. Themethod of claim 15, wherein the extended communication window ends afterthe non-extended communication window.
 18. The method of claim 15,wherein the extended communication window starts before and ends afterthe non-extended communication window.
 19. An apparatus comprising: alocal timer configured to generate a local representation of currenttime; a receiver configured to wirelessly receive a remote device'srepresentation of current time during a non-extended communicationwindow having a first window duration in which communication signalswith the remote device are communicated to synchronize a frequencyhopping sequence with the remote device; and circuitry configured tocompare the local and remote representations of current time, and inresponse to determining that the local and remote representations ofcurrent time differ by at least a predetermined amount, establishing anextended communication window with a second window duration in whichcommunications signals with the remote device will be communicated tosynchronize the frequency hopping sequence with the remote device,wherein the second window duration is longer than the first windowduration.
 20. The apparatus of claim 19, further comprising a sleepcontrol module configured to awaken the apparatus for communicationduring the non-extended communication window and the extendedcommunication window.